A 100 gigabit per second (Gbps) transport apparatus receives a 100 G Ethernet (registered trademark) (100 GE) client signal, for example, and maps the client signal to an optical-channel transport unit 4 (OTU4) transport frame by a framing processing unit. Then, the transport apparatus performs digital signal processing for performing signal equalization or the like by a signal processing unit, transfers an electrical signal output from the signal processing unit to an optical transceiver that performs electric-optic (E/O) conversion, converts the electrical signal into an optical signal by the optical transceiver, converts the optical signal into a 100 G line signal by means of modulation using dual polarization quadrature phase shift keying (DP-QPSK), and transfers the line signal.
In up-to 100 G transport apparatuses, generally, a client signal corresponding to 100 G is input, and a line signal corresponding to 100 G is output. In this case, one client signal is input and one line signal is output.
On the other hand, in forthcoming beyond-100 G transport apparatuses, for example, when 100 GE×3 client signals are input, 150 G signals modulated by means of 8-quadrature amplitude modulation (8 QAM) may be transported via a super-channel having two central wavelengths. By doing so, the same analog-to-digital converter (ADC) and digital-to-analog converter (DAC) as used in the 100 G transport apparatus can be used. In this case, three client signals are input and two line signals are output. A specific example of a transport frame is OTUk (k=1, 2, 3, 4) defined by ITU-T Recommendation G.709, “Interfaces for Optical Transport Network (OTN)” (Non-Patent Document 1).